The Nature of the Faint Chandra X-ray Sources in the Galactic Centre

Ashley J. Ruiter (1), Krzysztof Belczynski (1,2), and Thomas E. Harrison (1)

(1)New Mexico State University, Dept. of Astronomy, 1320 Frenger Mall, Las Cruces, NM 88003
(2) Tombaugh Fellow

Paper: ApJL submitted


EPrint Server: astro-ph/0511813


Recent Chandra observations have revealed a large population of faint X-ray point sources in the Galactic Centre. The observed population consists of 2000 faint sources in the luminosity range 1031-1033 erg s-1. The majority of these sources (70%) are described by hard spectra, while the rest are rather soft. The nature of these sources still remains unknown. Belczynski & Taam (2004) demonstrated that X-ray binaries with neutron star or black hole accretors may account for most of the soft sources, but are not numerous enough in order to account for the observed number and X-ray properties of faint hard sources. Both wind-fed systems and quiescent Roche lobe overflow transients were tested as potential source candidates. Muno et al. (2004) proposed that intermediate polars (subclass of magnetic cataclysmic variables) may be able to explain the faint hard population. Since an observational test of this hypothesis is not currently feasible due to (i) the large extinction toward the Galactic Centre, and (ii) low luminosity of intermediate polar donors (K-M dwarfs), we propose a theoretical test. A full population synthesis calculation of the Galactic Centre region has been carried out. Our results indicate that the numbers and X-ray luminosities of intermediate polars are consistent with the observed faint hard Galactic Centre population. We discuss the properties of the intermediate polar population, and suggest future tests for the hypothesis. For example, the derived slope of the X-ray luminosity function from our synthetic population of 0.8 could be compared with the observed slope, once one has been obtained from observations.

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